Phase evolution and thermophysical properties of high-entropy RE2(Y0.2Yb0.2Nb0.2Ta0.2Ce0.2)2O7 oxides

Pursuing novel thermal barrier-coating materials with lower thermal conductivity and high-temperature stability can simultaneously improve the working efficiency and service temperature of a gas turbine. In this study, a series of high-entropy RE2(Y0.2Yb0.2Nb0.2Ta0.2Ce0.2)(2)O-7 (RE = La, Nd, Sm, Gd, Dy, and Er) oxides were prepared though solid-state reaction. Through tuning the rare-earth cations, an order-disorder transition occurs from certain partially ordered weberite structure (C222(1)) to disordered defective fluorite structure (Fm3 over bar $\bar{3}$m). All the high-entropy RE2(Y0.2Yb0.2Nb0.2Ta0.2Ce0.2)(2)O-7 oxides possess low thermal conductivity in the range of 0.91-1.34 W m(-1) K-1 at room temperature, which can be attributed to increased lattice anharmonicity and disorder, resulting in additional phonon scattering. Herein, we proved that the incorporation of heterovalent cations at B-sites in high-entropy A(2)B(2)O(7) crystals is an effective strategy to reduce the thermal conductivity without compromising the decrease of oxygen vacancy. Moreover, the high-entropy RE2(Y0.2Yb0.2Nb0.2Ta0.2Ce0.2)(2)O-7 oxides show the relatively higher thermal expansion coefficients of 10.3-10.7 x 10(-6)degrees C-1 and excellent phase stability at elevated temperatures.